Automotive instrumentation clusters serve the useful function of providing a wealth of information about vehicle operation to the driver. Typically, the cluster provides primary operational information such as vehicle speed, engine speed and temperature, fuel level and oil pressure, in addition to providing secondary operational information regarding vehicle security (door ajar, etc.), use of seat belts, emissions, and the like.
Conventional instrument displays in automobiles are located in an area in front of the driver, below the windshield or windscreen which is normally referred to as the dashboard or instrument panel. As is well known, this arrangement requires drivers wishing to check their current rate of speed to momentarily lower their eyes so that they are focusing on the speedometer on the dashboard and not watching the road.
Prior art instrumentation clusters generally are quite large and bulky and require complex manufacturing equipment and processes. This is due to the size and quantity of hardware typically required for analog and digital instrumentation, such as motors, wiring and lighting.
For example, U.S. Pat. No. 3,636,447, issued to Gelenius, discloses a wide-angle electrical gauge having two coils. The two coils are angularly displaced at 90.degree. to each other. A circuit supplies current as approximate sine and cosine waves to the coils, resulting in a wide-angle displacement of an indicator needle.
U.S. Pat. No. 3,946,311, issued to Baker et al., discloses an air core gauge with an expanded pointer range. Pulse generators control a switching means so as to cause excitation of a plurality of angularly oriented coils. The excitation creates a resultant mmf vector, resulting in the displacement of a magnet and its associated pointer.
U.S. Pat. No. 4,890,027, issued to Bohner et al., discloses a dynamic motor controller for a high-performance, lightweight and low cost motor. The position control of the motor is accomplished by the use of an electronic braking apparatus, which includes a piezoelectric transducer for applying a braking force to the rotor.
U.S. Pat. No. 4,884,058, issued to Ikeda, discloses a combination indicator apparatus for an automotive vehicle. The indicator apparatus includes a plurality of cross-coil (air gauge) movements for use as analog indicators, the movement being driven by a single controller in a time-sharing serial transmission mode of operation.
U.S. Pat. No. 4,988,944, issued to Ito, discloses a cross coil type instrument wherein a plurality of coils are cross-arranged around a rotatable permanent magnet. The instrument further includes a needle secured to the magnet to rotate therewith. Rotation of needle is caused by a generated composite magnetic field.
Air core or cross-coil type gauges thus have distinct sizing, cost and efficiency disadvantages especially when utilized with projection-type instrumentation such as head-up displays (HUD's). These disadvantages are due primarily to the construction and control of the gauges.
For safety reasons and reasons of general convenience, it has been suggested that a head-up type display, similar to those found in fighter aircraft, be used in the environment of an automobile to provide the driver with a means for reading the automotive instrumentation without removing the driver's visual attention from the roadway.
It is considered impractical from the viewpoint of cost, to simply apply aircraft head-up display technology to the environment of an automobile. The cost of such a head-up display would be an appreciable fraction of the normal cost of the automobile. Thus, the benefits to be derived from a head-up display would not justify the cost of installing such a device.
Head-up displays of the type used in military aircraft occupy a substantial volume. A straightforward installation of an aircraft type head-up display would require either a large volume to be placed above the normal line of the automobile hood, or breaking throughout the firewall into the engine compartment in a manner which is deemed to be wholly impractical. Similarly, there is insufficient room between the firewall and the dashboard to allow practical redesign of an otherwise normal passenger automobile to accommodate a conventional head-up display. Thus, application of head-up display technology to the environment of an automobile requires a way to reduce the volume occupied by the display.
In contrast to the aviation setting, the automobile driver requires a relatively small amount of information, in a relatively small angular space, which is comfortably visible without head motion. A practical head-up display for an automobile should provide a fairly compact instrument cluster which is visible from any area in space in which a driver's eyes might be located.
In some ways the environment of a conventional passenger automobile is more harsh on such a display than the environment of a high performance fighter aircraft. In particular, a head-up display is one which includes an optical path from the display source to the combiner which is located at or near the windshield of the vehicle in which the display is installed. While military aircraft are treated with special care while parked on the ground and out of service, it is well known that automobiles are often left standing for extended periods of time in environments which range from extreme cold to extreme heat and sunlight.
The temperature within an automobile parked in the sun on a hot day, can easily exceed 140.degree. F. Furthermore, an optical path from the source, through the exit orifice up to the combiner, normally includes an axis which is substantially perpendicular to the ground. This means that when the sun is overhead, there is a small but finite probability that there may be a direct optical path coupling the sun back to the sources of the display image. This can lead to the focusing of very intense visible and infrared light rays at the display image which may damage the image source or projection. Therefore, heat dissipation at the image source of the display, as well as protection from the sunlight becomes an important factor.
One attempt to surface mount a coil gauge mechanism is disclosed in disclosure number 30650 contained in Research Disclosure, October, 1989. The gauge mechanism consists of surface mount coils and a permanent magnet spindle assembly. Attached to the spindle can be a dial pointer or other indicating device. The coils have a high permeability core and are wound with insulated copper wire for the coil. The rotational position of the spindle assembly permanent magnet is controlled by the amount and direction of electrical current in the surface mount coils. The mechanism is held in place by a bottom self-lubricating bearing and an upper bearing bracket. The upper bearing bracket also serves as a flux-containing package.